Monotonic Torsional Loading Test for the Evaluation of Low-Temperature Performance of Asphalt Binders

The research work presented in this paper focused on the evaluation of failure properties of asphalt binders at low temperatures by monotonic torsional loading (MTL) test. By making use of conventional dynamic shear rheometers, cylindrical specimens of binders (4 mm diameter and 5 mm height) were subjected to monotonic shear loadings until rupture at constant temperature and strain rate. The tests were performed at several temperatures and the brittleness index IB was calculated for the determination of the critical brittleness temperatures (Tcr). The investigated materials included four asphalt binders of different origins and types. For comparison purposes, the same binders were tested at the bending beam rheometer for the determination of their low-limiting performance grade (PG) temperature. Analysis of results was conducted with the primary goal of highlighting the differences in terms of performance ranking of materials obtained by using the two methods. The ranking order based on Tcr criterion appeared to be more coherent with the inherent nature of considered materials with respect to PG grading, revealing the ability of MTL test method in capturing the contribution of SBS polymer in enhancing thermal cracking performance of binder.